Mr. Hanna Bishara, Ph.D. Candidate

Detection of ultra-small mechanical pressures in an atmospheric environment is of a high technological interest in various applications such as medical diagnosis, gas leakage detection and artificial intelligence. The piezoelectric effect enables detection of a mechanical pressure by a change of the material dielectric polarization. This research reports on detection of ultra-small mechanical pressures in the scale of sub-Pascals at an atmospheric environment. For this purpose, low-k piezoelectric thin films and nanocrystals were grown with preferred crystallographic orientations on flexible metal substrates in order to improve sensitivity and reduce noise. Linear dielectric AlN thin films were deposited by using a rf reactive sputtering system on aluminum foils, where the aluminum grains have a preferred [100] crystallographic orientation in-vertical to the foil surface plane. Different preferred crystallographic orientations of the AlN grains relative to the film plane were formed at different deposition temperatures. High detection sensitivity to small mechanical pressures in the scale of 1 Pa was found in the AlN films having a unique preferred crystallographic orientation and negligible internal residual stress. A solid correlation between the crystallographic orientation of the AlN grains, the internal residual stress in the grains and the detection sensitivity of mechanical pressures was found. This correlation is presented and explained based on atomic bonds mismatch at the AlN film /Al foil interface. Moreover, the piezoelectric response of the AlN films to thermal strains was studied and found to be dependent on the residual stress magnitude in the film.

Non-linear dielectric Sodium Nitrite (SN) nanocrystals were grown by precipitation from a liquid solution inside nano-pores made of amorphous alumina. The SN crystals were grown with preferred crystallographic orientations along the longitudinal axis of the pores. All orientations exhibited a high sensitivity to ultra-low mechanical pressures (lower than 1 Pa), which depends on the crystallographic orientation of the SN crystals inside the pores. An asymmetric piezoelectric response to compressive vs. tensile applied pressures were found in the SN crystals and explained based on the molecular structure and dielectric polarizability.